Document text reference resolution rules

[dsheets]

(** Type of ordered address scope classifications *)
type scope =
| Point
| Interface
| Link
| Admin
| Site
| Organization
| Global
with sexp

(** A collection of functions for IPv4 addresses. *)
module V4 : sig
 (** [scope ipv4] is the classification of [ipv4] by the {! scope }
      hierarchy. *)
  val scope : t -> scope
end

The reference to scope in the doc for V4.scope ends up pointing to itself rather than to the unit-level scope.

[lpw25]

I guess we could special case the rules to resolve all other names in scope ahead of the name of the thing being documented.

[dsheets]

I think the rec case should be lowest priority.